(a) Field of the Invention
The present invention relates to a method of forming titanium silicide by heating a silicon substrate having a titanium film formed thereon. Moreover, the present invention relates to a method of measuring the temperature during the heating process.
(b) Description of the Background
Silicide is typically used to decrease contact resistance between a silicon substrate and a metal layer in semiconductor devices. More specifically, titanium silicide (TiSi.sub.2) is used in integrated circuit technologies because it has low resistivity and high thermal stability. Titanium silicide is formed by depositing a layer of titanium on a silicon substrate and subjecting the silicon substrate to a rapid and high thermal treatment known as rapid thermal process (RTP) which is well known in the art. The rapidness of the RTP process prevents impurities from defusing into the substrate. RTP of titanium formed on a silicon substrate, however, may result in a titanium silicide layer having an excessively high resistance value and resistance non-uniformity. Accordingly it is desirable to perform the RTP at a temperature which causes the titanium silicide layer to have a low and generally constant resistance value and resistance non-uniformity.
An optical sensor or an optical pyrometer is used to measure the temperature of the silicon substrate including the titanium or titanium/titanium silicide. The temperature is measured by making a visual comparison of luminance of specific wave length emitted from the silicon substrate with titanium or titanium/silicide to standard values. In order to be able to accurately measure the temperature, the optical sensor must be precisely calibrated. Accordingly, it is desirable to provide a method for accurately calibrating the optical sensor.